The term sarcopenia is defined as the loss of mass and muscular function with age. It is characterized by a metabolic status in which the muscles present a reduced ability to produce and use energy. Thus, in humans between 20 and 80 years of age, muscle mass decreases about 40%, with negative effects on mobility, strength production, metabolic rate and respiratory function. A continuous reparative process is also present in skeletal muscle due to the presence of quiescent adult stem cells, called satellite cells, which are able to change their phenotype when appropriate conditions are present.

What causes Sarcopenia?

1. The aging process
2. Physical inactivity
3. Reduction of hormone production in the human body as we age
4. i. Testosterone - ii. Human growth hormone Decrease of protein synthesis ability within the human body as we age
5. Female estrogen levels may also play a role in the development of sarcopenia during and after menopause. This topic has limited research, but it does appear that many females develop a “pouch” after menopause.

There are several causes of sarcopenia. Some are out of a person's control, like disease or environmental conditions. However, as it relates to advancing age, the condition is generally attributed to three factors: motor unit restructuring, protein deficiency and changes in hormone concentrations. While each of these factors is distinct, they actually combine to produce the age-related loss of muscle coordination and mass that we call sarcopenia.

Muscle mass is made up of proteins. The human body seeks a stasis between protein production (synthesis) and usage (metabolism) for energy and cellular structure. Our body can make some of these on its own; these proteins, built from amino acids, are called nonessential proteins because the body doesn't need to get them from an outside source. The proteins our bodies require that it can't produce by itself are called essential proteins. We derive these proteins from foods like peanut butter and tuna.

Making the clinical diagnosis of sarcopenia is difficult for the following reasons. There is no absolute level of lean mass, body cell mass, or muscle mass for comparison. There is no generally accepted clinical test to diagnose sarcopenia. Finally, there is no accepted threshold of functional decline at which sarcopenia is implied. However, the use of whole-body dual-energy X-ray absorptiometry (DEXA) or CT scans of the abdomen to assess muscle mass is being assessed in research settings. Baumgartner et al. published a working definition of sarcopenia based on 2 standard deviations below the mean for healthy young adults which has been used in research settings.